Method of separation of materials by the use of a membrane have been noted from the standpoint of saving resources and energy. Separation by membrane is applicable to a variety of materials including gases, such as oxygen and hydrogen. In separation of a mixed gas, if a specific gas in the mixed gas may be concentrated, various advantages are attained according to the kind of the gas.
Taking oxygen for an instance, it is said that use of an oxygen-rich air for combustion boilers will save 10% or more of a fuel. Further, medical use of an oxygen-rich air secures safety against accidental oxygen poisoning as encountered in the use of pure oxygen.
Materials which can be used for a membrane for separating oxygen are required to have (1) a great oxygen permeability coefficient, (2) high selectivity to oxygen permeation, (3) capability of forming a thin film, and the like. However, none of known materials satisfies both of the requirements (1) and (2) above at the same time. Therefore, in selecting materials for the membrane, it is general practice to consider predominantly either one of the above requirements (1) and (2) over another according to the end use of the membrane.
Materials that are superior in terms of oxygen permeability coefficient broadly include polycarbonate/polyorganosiloxane copolymers, poly-4-methylpentene-1, fluorine-containing polymer/polyorganosiloxane graft copolymers, phenol- or phenol ether-added polymer/.alpha.,.omega.-difunctional polysiloxane block copolymers, and the like. Polyphenylene ether is already known as an example of these materials.
Since the polyphenylene ether does not have a sufficient oxygen permeability coefficient, several attempts have been so far made in order to increase the oxygen permeability coefficient of the polyphenylene ether. For example, conventional techniques include a method for introducing a 2-allyl-6-methylphenylene ether unit or a 2,6-diallylphenylene ether unit into at least a part of the repeating unit as disclosed in Japanese Patent Application (OPI) No. 55008/83 (the term "OPI" as herein used means "unexamined published application") and a method for blending a polyphenylene ether and a polyorganosiloxane as disclosed in Japanese Patent Application (OPI) No. 95538/83. However, these known methods are still unsatisfactory. In particular, the latter method involves a disadvantage of poor compatibility between a polyphenylene ether and a polyorganosiloxane.